The present invention relates to pressurized liquid storage reservoirs of the type comprising a liquid outlet passage having a surface tension retention device defining a buffer zone communicating with said outlet passage and, through orifices and a liquid meniscus breakage zone, with supply channels provided along the wall of the reservoir.
The invention finds a particularly important application in the storage of ergol propellant on board a space vehicle which, during part at least of its orbiting flight, is subjected to only negligible acceleration and gravity whose direction relative to the reservoir may vary. The low point of the reservoir then changes, so that the outlet passage cannot be placed there in such a way that it is permanently fed. Two solutions have been adopted to make a minimum volume of liquid permanently available after a phase of zero gravity operation. A first solution consists in fractionating the reservoir into a variable volume compartment, constantly filled with liquid, and a pressurization gas compartment by means of a diaphragm. Unfortunately, the diaphragms at present available are not compatible with all ergols to a sufficient degree in the long term. A second solution consists in providing the reservoir with ergol retention means which use surface tension for forming, about a draw-off point, a buffer zone storing a volume of single phase ergol and preventing pressurization gas from escaping with the ergol, which gas would affect operation of the nozzles fed by the reservoir.
Most of the retention means in current use comprise capillary passages defined by blades, for they have characteristics (and more especially a maximum pressure difference before breakage of the gas-liquid interface meniscus) which are more uniform and more reproducible because they are more easily cleaned and resist corrosion better than fabrics.
A prior art bladed retention device (French specification No. 2 486 624) comprises a central volume surrounded by a capillary structure formed from radially directed elements which define capillary spaces of a width increasing outwardly. This arrangement has disadvantages and limitations in use. It leads to a large central volume which cannot be drawn off, for the elements can only be extended inwardly in the radial direction within a limit fixed by a minimum width of the capillary spaces. Moreover, some flights may involve high rotational speeds of the vehicle about axes of orientation such that the ergol occupying the buffer zone is forced towards zones from which the retention device cannot be reprimed.
It is an object of the invention to provide a storage reservoir of the above defined type comprising improved retention means. It is a more particular object to provide a device in which a small volume only cannot be drawn. It is an object to substantially eliminate conditions for which the device fails to operate on a satellite.
To this end, there is provided a storage reservoir wherein the orifices are capillary and are provided in a wall situated in the immediate proximity of the point of drawing-off through the outlet passage, which wall defines, with a capillary storage volume, a dead space of comparatively small volume.
The capillary storage volume will generally be in the form of a plurality of substantially coaxial thin annular zones, split up into passages developing in the circumferentially direction of the same order of size as the thickness. These annular zones of the alternating smooth walls and corrugated walls may be defined by a spirally wound strip, the spacing between two turns being fixed by a corrugated sheet. In another embodiment, the annular zones are defined by smooth concentric cylindrical metal shapes, centered by means of corrugated strips.
So as to improve the resistance to transverse accelerations, caused for example by rotation of the space vehicle, the capillary storage volume is advantageously contained in a casing comprising a gas exhaust opening situated on the opposite side to the drawing-off point. This opening will be generally extended by a duct opening in the vicinity of the wall of the reservoir in a region thereof which forms the low point when the reservoir is subjected to a high transverse accelaration.
The meniscus rupture zone, placed around the dead space, will be at a very small distance from the axis of the device, which increases the acceleration threshold likely to cause unpriming of the buffer zone. This rupture zone communicates with the inside of the reservoir through passages formed along the wall by collection and resupply blades. It also communicates with the inside of the reservoir, under the bottom of the casing one face at least of which is made from an unwettable material or which provides confinement decreasing towards the opening into the reservoir through gas removal passages.
The invention will be better understood from reading the following description of particular embodiments thereof, given by way of examples.